EP0605908A2

EP0605908A2 - Water insoluble manganese particles as magnetic resonance, imaging contrast enhancement agents

Info

Publication number: EP0605908A2
Application number: EP93203303A
Authority: EP
Inventors: Kenneth E. C/O Sterling Winthrop Inc. Kellar; Elaine C/O Sterling Winthrop Inc. Liversidge; Wolfgang H.H.O Sterling Winthrop Inc. Gunther; Gregory L. C/O Sterling Winthrop Inc. Mcintire; Barbara C/O Sterling Winthrop Inc. Vanorman; Piotr H Eastman Kodak Company Karpinski
Original assignee: Eastman Kodak Co; Nanosystems LLC; Sterling Winthrop Inc
Current assignee: Nanosystems LLC
Priority date: 1992-12-17
Filing date: 1993-11-26
Publication date: 1994-07-13
Also published as: CZ265093A3; HUT65884A; NO934334L; IL107816A0; AU4885093A; JPH06199703A; EP0605908A3; NO934334D0; MX9306625A; KR940013538A; NZ248812A; CN1102348A; US5401492A; HU9303489D0; SK142693A3; FI935309A; FI935309A0; CA2107695A1

Abstract

A magnetic resonance imaging composition for imaging of an organ rich in mitochondria comprising particles of a substantially insoluble manganese salt is described, together with a method of preparing the composition, which advantageously also contains a surfactant, which comprises contacting a manganese source with a counter ion source for a time and under conditions sufficient for the formation of said insoluble manganese salt. Preferably the organ rich in mitochondria is the liver, the particles are substantially nonmagnetic with a preferred particle size of less than about 10 microns and the insoluble manganese salt selected from the group consisting of manganese phosphate and manganese carbonate.

A method of diagnosis comprising administering to a mammal a contrast effective amount of a composition of the particles is also described.

Description

FIELD OF THE INVENTION

This invention relates to diagnostic compositions useful in magnetic resonance imaging. More particularly, this invention relates to water insoluble manganese particles that can be used in magnetic resonance imaging of organs.

BACKGROUND OF THE INVENTION

The enhancement of positive contrast in the magnetic resonance (MR) image of an organ rich in mitochondria, such as the liver, pancreas, or kidney, requires an agent that specifically locates in those organs and causes an increase in the longitudinal relaxation rate of water protons in those organs. The increase in the relaxation rate, which is responsible for enhancing positive contrast, is due to a dipolar interaction between the magnetic moments of the water protons and the magnetic moments of the paramagnetic contrast enhancement agent. The increase in the relaxation rate per unit concentration of paramagnetic contrast enhancement agent is called the relaxation efficiency, or relaxivity, of the agent.
Runge et al., U.S. Patent No. 4,615,879 discloses a contrast media composition for nuclear magnetic resonance (NMR) imaging of the gastrointestinal tract. The compositions prepared in that invention provided a decrease in both the spin lattice (Ti) and the spin-spin (T₂) relaxation time of protons, thereby increasing the imaging of the gastrointestinal tract.
However, it would be desirable to have a composition for MR imaging which, in its native form, did not affect proton T₁ and T₂, that is, a composition which is substantially nonmagnetic, and which becomes a contrast agent upon in vivo administration. The present invention provides for a MR imaging composition for MR imaging of organs such as the liver.

BRIEF DESCRIPTION OF THE INVENTION

According to the present invention there is provided a magnetic resonance imaging composition for imaging of an organ rich in mitochondria comprising particles of a substantially insoluble manganese salt. In a preferred embodiment, the organ rich in mitochondria is the kidney, pancreas, biliary network or preferably the liver. In a further preferred embodiment, the particles are substantially nonmagnetic, more preferably having a particle size of less than about 10 microns.
The insoluble manganese salt is preferably selected from the group consisting of manganese phosphate and manganese carbonate and advantageously the composition of the present invention further comprises a surfactant.
In another aspect of the present invention there is provided a method of preparing a magnetic resonance imaging composition useful for imaging an organ rich in mitochondria comprising particles of a substantially insoluble manganese salt which comprises contacting a manganese source, preferably a manganese (II) source, with a counter ion source for a time and under conditions sufficient for the formation of said insoluble manganese salt. In a preferred embodiment, the contacting is by simultaneous admixing in an aqueous solution.
Preferably the manganese source is an aqueous solution of a soluble manganese (II) salt, more preferably selected from the group consisting of manganese acetate, manganese flouride or especially manganese chloride, manganese nitrate and manganese sulfate.
Advantageously the counter ion source is an aqueous solution of a carbonate salt, preferably selected from the group consisting of sodium carbonate, potassium carbonate, and ammonium carbonate; or an aqueous solution of a phosphate salt, preferably selected from the group consisting of sodium phosphate, potassium phosphate, and ammonium phosphate.
The present invention is also directed to a method of diagnosis comprising administering to a mammal a contrast effective amount of particles of a substantially insoluble manganese salt suspended or dispersed in a physiologically tolerable carrier and generating an NMR image of said mammal.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows the change in relaxivity of the tissue with time from 0 to 500 minutes after injection of the insoluble manganese particles of the present invention;
Figure 2 shows the change in relaxivity of the tissue with time from 0 to 9000 minutes after injection of the insoluble manganese particles of the present invention; and
Figure 3 shows the effect of surfactant coatings on the relaxation rate of the liver following injection into the tail veins of test animals of various dosages of insoluble manganese particles of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates to a magnetic resonance imaging composition comprising particles of a substantially insoluble manganese salt. In addition it is believed that the invention can be practised with particles of other substantially insoluble compounds or salts.
The relaxivity of a contrast enhancement agent in an organ such as the liver is not necessarily the same as the relaxivity of the agent in a beaker of water. Although the relaxivities of various manganese-containing agents are different in water, these agents have the same relaxivity in liver homogenates.
Although not wishing to be bound by theory, this similarity of relaxivities in liver homogenates suggests that manganese-containing agents are merely vehicles that deliver manganese to the liver, where the manganese is stripped from the agent and becomes bound to some macromolecule in the liver. It is the relaxivity of the manganese-liver macromolecule complex that is related to the enhancement of positive contrast in a liver MR image.
Although manganese is a targeting vector to organs such as the liver, not all of the injected dosage of manganese localizes in the liver. Manganese has been found in other organs as well.
One way of increasing liver specificity is to use water-insoluble manganese particles as contrast enhancement agents according to the composition of the present invention. Examples would include, but are not limited to, water-insoluble inorganic salts such as manganese phosphate or manganese carbonate. In general, water-insoluble particles with diameters ranging from about one hundred nanometers to a few micrometers are known to be taken up rapidly in the liver. Water-insoluble iron particles, which have a large T₂ (transverse relaxation time) effect on water protons under imaging conditions are currently being investigated as negative contrast enhancement agents for liver MR imaging. Unlike their iron counterparts, manganese particles do not significantly affect T₁ or T₂ of water protons. Any possible affect on T₁ or T₂ would be due to free manganese ions as a result of a solubility product. This effect can be removed by encapsulation of the manganese particles.
However, once localized in the liver, the manganese particle dissolves and releases manganese to form a manganese-liver macromolecule complex with a high relaxivity as hereinbefore explained. In summary, water-insoluble manganese particles afford higher liver specificity than water-soluble manganese chelates. As a result, the dosage of manganese required to enhance positive contrast in a liver MR image to a given extent will be less for water-insoluble manganese particles than for water-soluble manganese chelates.
The present invention is directed to a magnetic resonance imaging composition for imaging of organs rich in mitochondria comprising particles of a substantially insoluble manganese salt which, in its native form, is substantially nonmagnetic.
The residue of the particles is visualized by imaging that tissue with a magnetic resonance imaging system. The visualization of the residue of the particles can be accomplished with commercially available magnetic imaging systems such as a General Electric 1.5 T Signa imaging system [' H resonant frequency 63.9 megahertz (Mhz)]. Commercially available magnetic resonance imaging systems are typically characterized by the magnetic field strength used, with a field strength of 2.0 Tesla as the current maximum and 0.2 Tesla as the current minimum.
For a given field strength, each detected nucleus has a characteristic frequency. For example, at a field strength of 1.0 Tesla, the resonance frequency for hydrogen is 42.57 Mhz; for phosphorus-31 it is 17.24 Mhz; and for sodium-23 it is 11.26 Mhz.
As used herein, the phrase "organs rich in mitochondria" refers to organ systems in the body of a mammal which contain an abundance of the organelle called mitochondria. One measure of mitochondrial abundance is the level of mitochondrial enzymes present in a particular organ system. Organs rich in mitochondria include the liver, kidney, pancreas and biliary network. Preferred organs rich in mitochondria include the liver and kidney. A more preferred organ rich in mitochondria is the liver.
In a preferred embodiment, the particles of the present invention, in their native form, are substantially nonmagnetic. That is, the particles have no effect on T₁ or T₂ as composed ex vivo. Once the particles are used in the diagnosis of a mammal, according to the methods of the present invention, the Mn within the particles is liberated to form a Mn bioconjugate, as discussed elsewhere herein.
In a further preferred embodiment, the particles of the present invention have a particle size of less than about 10 microns. As used herein, the phrase "particle size" refers to a mean particle size as measured by conventional particle size measuring techniques well known to those skilled in the art, such as sedimentation field flow fractionation, photon correlation spectroscopy, disk centrifugation, or scanning electron microscopy (SEM). The phrase "particle size of less than about 10 microns" as used herein means that at least 90% of the particles have a particle size of less than about 10 microns when measured by the above- noted techniques. It is preferred that at least 95%, more preferably at least 99%, of the particles have a particle size of less than about 10 microns. A preferred particle size is less than about 5 microns, more preferably less than about 2.5 microns.
The insoluble manganese salt yields manganese ions when in solution. Preferred manganese salts include manganese oxide, manganese dioxide, manganese iodate, manganese oxalate, manganese hydroxide, manganese hydrogen phosphate, manganese sulfide, manganese phosphate, manganese carbonate, manganese bile salts such as manganese oleate, manganese stearate, manganese cholate, and manganese taurocholate, and manganese salts of various fatty acids, and the like. Particularly preferred manganese salts are manganese phosphate and manganese carbonate.
As used herein, the phrase "substantially insoluble manganese salt" refers to a manganese salt with a solubility product (Ksp) of less than about 1x10^-6. Preferably the Ksp is less than about 5x1 0-7. Manganese salts useful as a substantially insoluble manganese salt have Ksp values as follows: manganese iodate (4.4x10-⁷), manganese oxalate (1.7x10-⁷), manganese hydroxide (2.1x10^-13), manganese hydrogen phosphate (1.4x10-¹³),manganese sulfide (4.7x1 0-14) and manganese carbonate (2.2x10-11). The solubility in plasma or in vivo may affect the preferred timing of imaging.
In another preferred embodiment, the composition of the present invention may contain a surfactant. Preferred surfactants include Pluronic F68 NF and Pluronic F-108, both of which are block copolymers of ethylene oxide and propylene oxide, dimyristoylphosphatidylglycerol (DMPG), Tetronic 908 and Tetronic 1508, both of which are tetrafunctional block copolymers derived from sequential addition of proylene oxide and ethylene oxide to ethylenediamine, Tween 20 and Tween 80, both of which are polyoxyethylene sorbitan fatty acid esters, Tyloxapol, which is a polymer of the alkyl aryl polyether alcohol type, Henkel APG 325cs, polyvinyl alcohol, polyvinyl-pyrrolidone PVP K-15, dioctylsulfosuccinate (DOSS) and OMLF108, which is a blocked copolymer of ethylene oxide and propylene oxide linked through a methylene group. Particularly preferred surfactants include DMPG, Pluronic F68 NF and especially DOSS.
The present invention is further directed to a method of preparing the magnetic resonance imaging composition comprising contacting a manganese source with a counter ion source. Such counter ions are typically anions which interact with the manganese cation to form an insoluble manganese salt.
As used herein, the phrase "a manganese source" refers to an aqueous solution which contains free manganese ions, that is, manganese ions available for chemical reaction. For example, an aqueous solution of manganese chloride would contain free manganese ions available for chemical reaction. The manganese ion source need not contain the counter ion, in this case, chloride, to be useful in the processes of the present invention.
A preferred manganese source is a soluble or insoluble manganese salt. Preferred soluble manganese salts include manganese chloride, manganese nitrate, manganese sulfate, manganese acetate, manganese fluoride, and the like. Other exemplary soluble manganese salts may be found in the Handbook of Chemistry and Physics, CRC Press, Cleveland, OH. The manganese source may contain a nontoxic ionic additive, e.g. ammonium chloride and/or aluminium sulphate to prevent agglomeration.
As used herein, the phrase "a counter ion source" refers to an aqueous solution which contains a free counter ion, that is, a counter ion which is available for chemical reaction. For example, an aqueous solution of sodium carbonate would contain free carbonate counter ions available for chemical reaction. The carbonate counter ion need not contain any other ions, in this case sodium, to be useful in the processes of the present invention.
A preferred counter ion source is a soluble carbonate or phosphate salt. Preferred soluble carbonate salts include sodium carbonate, potassium carbonate, and ammonium carbonate. Preferred soluble phosphate salts include sodium phosphate, potassium phosphate, and ammonium phosphate. Other exemplary soluble carbonate and phosphate salts may be found in the Handbook of Chemistry and Physics, CRC Press, Cleveland, OH.
Another preferred counter ion source includes aqueous solutions of the salts of oleic and cholic acid.
In a preferred embodiment, contacting of the manganese ion source and the counter ion source is by simultaneous admixing in an aqueous solution. This aqueous solution is sometimes referred to herein as the "host solution", that is, the solution into which the manganese ion source and counter ion source are simultaneously admixed.
The host solution may contain other buffers, salts, or surfactants useful in the processes of the present invention. For example, the host solution may contain citric acid, sodium citrate, ascorbic acid or other acids, bases or buffers to regulate the pH value of the host solution. Additionally, the host solution may contain a variety of surfactants and stabilizers, as is well known in the art. Several of these surfactants and stabilizers have been discussed elsewhere herein.
In brief, using the processes of the present invention, suspensions of manganese particulates, are prepared by a double-jet precipitation technique, i.e. by an addition of two reagents, each at a predetermined flow rate, into a vessel containing an aqueous host solution. The host solution may, in addition to water, contain additives (i.e. growth and crystal morphology modifiers), suspension stabilizing additives (stabilizers), and surfactants. The precipitation can take place at a temperature from 1 to about 95 _°C, preferably 4 to 30 _° C. In preferred embodiments, the temperature of the contents of the reaction vessel is controlled to within +/- 2.0 _°C, more preferably +/- 0.5 _°C.
In accordance with the present invention, the rate of reagents' addition is determined from the stoichiometry of the underlying chemical reaction(s). As complete precipitation of Mn cation as determined by equilibria is desirable therefore, the other reagent is added in a slight to moderate excess.
In the present invention, the size, size distribution, morphology, and the degree of agglomeration of precipitated manganese particles is manipulated by the use of specific addition rates, initial volume of the host solution, and addition of certain additives, such as electrolytes, stabilizers, and surfactants to the host solution and/or to either or both reagents.
Furthermore, the duration of the reagent addition is determined by the desired final solid content and the volume of the suspension, and the addition rate applied. The addition rate can be maintained by any means of volumetric or gravimetric flow rate control, such as a manual or automatic (including computer- driven) pump speed or displacement control or by control of the hydrostatic pressure of the reagents.
In the method of diagnosis comprising administering the particles of the invention, suspended or dispersed in a carrier, to a mammal, a contrast effective amount of particles is that amount necessary to provide tissue visualization with magnetic resonance imaging. Means for determining a contrast effective amount in a particular subject will depend, as is well known in the art, on the nature of the magnetically active material used, the mass of the subject being imaged, the sensitivity of the magnetic resonance imaging system and the like.
After administration of these particles, the subject mammal is maintained for a time period sufficient for the administered particles to be distributed throughout the subject and enter the tissues of the mammal. Typically, a sufficient time period is from about 5 minutes to about 8 hours and, preferably from about 10 minutes to about 90 minutes. The residue of the particles is visualized by imaging that tissue with a magnetic resonance imaging system.
The present invention includes the particles described above formulated into compositions together with one or more non-toxic physiologically acceptable carriers, adjuvants or vehicles which are collectively referred to herein as carriers, for parenteral injection, for oral administration in solid or liquid form, for rectal or topical administration, or the like.
The compositions can be administered to humans and animals either orally, rectally, parenterally (intravenous, intramuscular or subcutaneous), intracisternally, intravaginally, intraperitoneally, locally (powders, ointments or drops), or as a buccal or nasal spray.
Compositions suitable for parenteral injection may comprise physiologically acceptable sterile aqueous or nonaqueous solutions, dispersions, suspensions or emulsions and sterile powders for reconstitution into sterile injectable solutions or dispersions. Examples of suitable aqueous and nonaqueous carriers, diluents, solvents or vehicles include water, ethanol, polyols (propyleneglycol, polyethyleneglycol, glycerol, and the like), suitable mixtures thereof, vegetable oils such as olive oil and injectable organic esters such as ethyl oleate. Proper fluidity can be maintained, for example, by the use of a coating such as lecithin, by the maintenance of the required particle size in the case of dispersions and by the use of surfactants.
These compositions may also contain adjuvants such as preserving, wetting, emulsifying, and dispensing agents. Prevention of the action of microorganisms can be ensured by various antibacterial and antifungal agents, for example, parabens, chlorobutanol, phenol, sorbic acid, and the like. It may also be desirable to include physiological salts, dextran, and isotonic agents, for example sugars, sodium chloride and the like. Prolonged absorption of the injectable pharmaceutical form can be brought about by the use of agents delaying absorption, for example, aluminum monostearate and gelatin.
Solid dosage forms for oral administration include capsules, tablets, pills, powders and granules. In such solid dosage forms, the active compound is admixed with at least one inert customary excipient (or carrier) such as sodium citrate or dicalcium phosphate or (a) fillers or extenders, e.g. starches, lactose, sucrose, glucose, mannitol and silicic acid, (b) binders, e.g. carboxymethylcellulose, alignates, gelatin, polyvinylpyrrolidone, sucrose and acacia, (c) humectants, e.g. glycerol, (d) disintegrating agents, e.g. agar-agar, calcium carbonate, potato or tapioca starch, alginic acid, certain complex silicates and sodium carbonate, (e) solution retarders, e.g. paraffin, (f) absorption accelerators, e.g. quaternary ammonium compounds, (g) wetting agents, e.g. cetyl alcohol and glycerol monostearate, (h) adsorbents, e.g. kaolin and bentonite, and (i) lubricants, e.g. talc, calcium stearate, magnesium stearate, solid polyethylene glycols, sodium lauryl sulfate or mixtures thereof. In the case of capsules, tablets and pills, the dosage forms may also comprise buffering agents.
Solid compositions of a similar type may also be employed as fillers in soft and hard-filled gelatin capsules using such excipients as lactose or milk sugar as well as high molecular weight polyethyleneglycols, and the like.
Solid dosage forms such as tablets, dragees, capsules, pills and granules can be prepared with coatings and shells, such as enteric coatings and others well known in the art. They may contain opacifying agents, and can also be of such composition that they release the active compound or compounds in a certain part of the intestinal tract in a delayed manner. Examples of embedding compositions which can be used are polymeric substances and waxes.
The active compounds can also be in micro-encapsulated form, if appropriate, with one or more of the above-mentioned excipients.
Liquid dosage forms for oral administration include pharmaceutically acceptable emulsions, solutions, suspensions, syrups and elixirs. In addition to the active compounds, the liquid dosage forms may contain inert diluents commonly used in the art, such as water or other solvents, solubilizing agents and emulsifiers, as for example, ethyl alcohol, isopropyl alcohol, ethyl carbonate, ethyl acetate, benzyl alcohol, benzyl benzoate, propyleneglycol, 1,3-butyleneglycol, dimethylformamide, oils, in particular, cottonseed oil, groundnut oil, corn germ oil, olive oil, castor oil and sesame oil, glycerol, tetrahydrofurfuryl alcohol, polyethyleneglycols and fatty acid esters of sorbitan or mixtures of these substances, and the like.
Besides such inert diluents, the composition can also include adjuvants, such as wetting agents, emulsifying and suspending agents, sweetening, flavoring and perfuming agents.
Suspensions, in addition to the active compounds, may contain suspending agents, as for example, ethoxylated isostearyl alcohols, polyoxyethylene sorbitol and sorbitan esters, microcrystalline cellulose, aluminum metahydroxide, bentonite, agar-agar and tragacanth, or mixtures of these substances, and the like.
Compositions for rectal administrations are preferably suppositories which can be prepared by mixing the compounds of the present invention with suitable non-irritating excipients or carriers such as cocoa butter, polyethyleneglycol or a suppository wax, which are solid at ordinary temperatures but liquid at body temperature and therefore, melt in the rectum or vaginal cavity and release the active component.
Dosage forms for topical administration of a compound of this invention include ointments, powders, sprays and inhalants. The active component is admixed under sterile conditions with a physiologically acceptable carrier and any preservatives, buffers or propellants as may be required. Ophthalmic formulations, eye ointments, powders and solutions are also contemplated as being within the scope of this invention.
Actual dosage levels of active ingredients in the compositions of the present invention may be varied so as to obtain an amount of active ingredient that is effective to obtain a desired diagnostic response for a particular composition and method of administration. The selected dosage level therefore depends upon the desired diagnostic effect, on the route of administration, on the desired duration of contrast and other factors. Dosages up to about 5 mmol/kg bodyweight are believed to be useful.
The invention will now be illustrated with reference to the following examples but the scope is in no way to be construed as limited thereto.

Example 1. Manganese Carbonate

50 g water, 100 mg anhydrous citric acid, and 400 mg Pluronic F-68 NF surfactant (altogether = host solution) were added to a 100 ml beaker, mixed with a magnetic bar, placed in a 40 _°C water bath to facilitate dissolution, and subsequently cooled to the room temperature. To the host solution was added a 1.0 M solution of MnC1₂ (manganese source) at a controlled rate of 4.0 ml/min. Simultaneously, a 1.02 M solution of Na₂C0₃ (carbonate source) was added thereto at a controlled rate of 4.8 ml/min. Each addition was maintained for 1.0 minute. The final pH was adjusted to pH 7.2-7.7. The resultant suspension contained a uniform, spherilitic crystalline precipitate of the mean grain diameter being 400 nm, as measured by a scanning electron microscopy (SEM). The free manganese concentration of this suspension, measured by an inductively coupled plasma atomic emission spectroscopy (ICP-AES), was less than 90 ug/ml.
Variations of the above formula, each resulting in similar or different suspension density, morphology of precipitate, mean size, size distribution, the concentration of free manganese, and the degree of particle agglomeration are as follows:-
The manganese source can be any other water-soluble salt of manganese, such as Mn(N0₃)₂, MnS0₄, MnF₂, manganese acetate, etc., and may contain a nontoxic ionic additive, e.g. 0.5 g NH₄CI and/or 0.68 g A1₂(SO₄)₃.18H ₂0, to prevent agglomeration.
The carbonate source may be any other water-soluble carbonate, such as ammonium carbonate, potassium carbonate, etc.
The host solution may be (a) water, (b) water and citric acid, (c) water and sodium citrate, (d) as in Example 1, except that the concentration of Pluronic surfactant may vary from 0-5 wt.%, (e) as in Example 1, except that Pluronic surfactant is replaced by any or a mixture of nontoxic surfactant or stabilizers, such as: DMPG, Tetronic 908, Tween 20, Tween 80, Pluronic F-108, Tyloxapol, Henkel APG 325cs, polyvinyl alcohol, PVP k-15, ascorbic acid, etc., whose concentration may vary from 0-5 wt%, (f) any variation given above and an ionic additive, such as NH₄CI, Al₂(SO₄)₃.18H₂O, in the amount of 0-1 wt%.
The surfactants, stabilizers, and/or ionic additives listed above, and/or citric acid, and/or sodium citrate, may be added to one, two or all three of the following: the manganese source, the carbonate source and the host solution.
The concentration of reagents, and/or the flow rates, and/or the time of addition may be different from that given in Example 1.

Example 2. Manganese(II) Phosphate

50 g water, 100 mg anhydrous citric acid, and 400 mg Pluronic F68 NF surfactant were added to a 100ml beaker, mixed with a magnetic bar, placed in a 40°C water bath to facilitate dissolution, and subsequently cooled to the room temperature. To this host solution was added a 1.0 M solution of MnC1₂ at a controlled rate of 4.0 ml/min. simultaneously, a 0.68 M solution of Na3PO4 was added thereto at a controlled rate of 6.0 ml/min. Each addition was maintained for 1.0 minute. The final pH was adjusted to pH 7.2-7.7. The resultant suspension contained a crystalline precipitate of the mean grain size being 150 nm, as measured by SEM. The suspension's free manganese concentration measured by ICP-AES, was less than 10 µg/ml.
Variations of the above formula, each resulting in similar or different suspension density, morphology of precipitate, mean size, size distribution, the concentration of free manganese, and the degree of particle agglomeration are as follows:

The manganese source and the host solution may be varied as described hereinbefore for Example 1.

The phosphate source may be any other water-soluble phosphate such as sodium phosphate, dibasic; sodium phosphate, monobasic; potassium phosphate, dibasic; potassium phosphate, monobasic; ammonium phosphate, dibasic; ammonium phosphate, monobasic; etc.
The surfactants, stabilizers, and/or ionic additives listed above, and/or citric acid, and/or sodium citrate, may be added to one, two or all three of the following: the manganese source, the phosphate source and the host solution.
The concentration of reagents, and/or the flow rates, and/or the time of addition may be different from that given in Example 2.

Example 3

Several of the formulations from the above Examples 1 and 2 were examined for their size, zeta potential (ZP), plasma stability, and whether the particular compositions could be autoclaved. The results of these studies are shown in Table 1.

Example 5

The hepatic clearing of manganese particles made in accordance to the processes of the present invention was tested. Animals were injected via the tail vein with 50 amol/kg bodyweight with manganese particles. At various times thereafter, the animals were euthanized and the livers of the animals were excised. Livers were frozen until assay, and then homogenized prior to the assay.
The results of these experiments are shown in Figures 1 and 2. In Figure 1, the time course of hepatic clearance was studied from 0 to 500 minutes after administration of the manganese particles. In Figure 2, the time course of hepatic clearance was studied from 0 to 9000 minutes after administration.

Example 6

The effects of surfactant coatings on the relaxation rate of the liver was studied using manganese particles prepared in accordance with the processes of the present invention. Animals were injected via the tail vein with the particles at various doses ranging from 5 amol/kg body weight to 200 µmol/kg bodyweight. After 30 minutes, the animals were euthanized, and the livers were excised. Livers were homogenized 1:1 (w/v) with saline, and then the relaxation rate of the homogenate was determined. The results are shown in Figure 3.

Example 7

The compositions of the invention produced impressive images of the liver. A formulation of manganese carbonate particles stabilized with DMPG provided optimal imaging 5 to 30 minutes post injection. A formulation of manganese carbonate particles stabilized with Pluronic F68 provided optimal imaging 30 minutes to 2 hours post injection.

Claims

1. A magnetic resonance imaging composition for imaging of an organ rich in mitochondria comprising particles of a substantially insoluble manganese salt.

2. A composition as claimed in claim 1 wherein said organ rich in mitochondria is the liver, kidney, pancreas or biliary network.

3. A composition as claimed in either of the preceding claims wherein said particles are substantially nonmagnetic.

4. A composition as claimed in any one of the preceding claims wherein said particles have a particle size of less than about 10 microns.

5. A composition as claimed in claim 4 wherein said particles have a particle size of less than about 5 microns.

6. A composition as claimed in any one of the preceding claims wherein said insoluble manganese salt is selected from the group consisting of manganese phosphate and manganese carbonate.

7. A composition as claimed in any one of the preceding claims further comprising a surfactant.

8. A composition as claimed in claim 7 wherein said surfactant is dioctylsulfosuccinate.

9. A composition as claimed in claim 7 wherein said surfactant is dimyristoylphosphatidylglycerol.

10. A composition as claimed in claim 7 wherein said surfactant is a block copolymer of ethylene oxide and propylene oxide.

11. A method of preparing a magnetic resonance imaging composition useful for imaging an organ rich in mitochondria comprising particles of a substantially insoluble manganese salt which comprises contacting a manganese source with a counter ion source for a time and under conditions sufficient for the formation of said insoluble manganese salt.

12. A method as claimed in claim 11 wherein said contacting is by simultaneous admixing in an aqueous solution.

13. A method as claimed in either of claims 11 and 12 wherein said manganese source is an aqueous solution of a soluble manganese (II) salt.

14. A method as claimed in claim 13 wherein said soluble manganese salt is selected from the group consisting of manganese chloride, manganese nitrate, manganese sulfate, manganese acetate and manganese flouride.

15. A method as claimed in any one of claims 11 to 14 wherein said counter ion source is an aqueous solution of a carbonate salt.

16. A method as claimed in claim 15 wherein said carbonate salt is selected from the group consisting of sodium carbonate, potassium carbonate, and ammonium carbonate.

17. A method as claimed in any one of claims 11 to 14 wherein said counter ion source is an aqueous solution of a phosphate salt.

18. A method as claimed in claim 17 wherein said phosphate salt is selected from the group consisting of sodium phosphate, potassium phosphate, and ammonium phosphate.

19. A method as claimed in any one of claims 11 to 14 wherein said counter ion source is an aqueous solution of a salt of oleic or cholic acid.

20. A method of diagnosis comprising administering to a mammal a contrast effective amount of the particles as claimed in claim 1 suspended or dispersed in a physiologically tolerable carrier and generating an NMR image of said mammal.